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How to Take Calibration Frames: Darks, Flats, Bias, Flat Darks...

Astrophotography calibration frames are extremely important if you're aiming to get the best possible images of deep sky objects. Although they make complete sense and become second nature once you are used to them, the different types of calibration frames can be very confusing to beginners.

Guide to calibration frames for astrophotography

While "light" frames are simply the name used to refer to our regular images, darks, bias, flats and dark flats are what we call "calibration frames." These are used to enhance the quality of our data by reducing the noise, getting rid of small artifacts, and taking care of vignetting around the edges.

Below, we go over how to take each of these frames.


Light Frames

Let's get this one out of the way right at the beginning: Light frames are not calibration frames. Light Frames are simply what your regular raw pictures are called. When importing all your raw data into your stacking software, for example PixInsight, you will add your files using the "Add Lights" button.

Master file for the Andromeda Galaxy
A typical stretched Master Light file before processing.

Now that this is clear, let's jump to the actual calibration frames. If you're unsure as to how many calibration frames to take for each category, we usually take 15 which works well.


Dark Frames

Dark frames are taken in complete darkness, when no light can reach the sensor. This is done by placing the cap of the camera (or the telescope if you do not wish to remove the camera from the camera) on. Darks help reduce the noise in our data, although new sensors are such low noise that darks are becoming less and less crucial.

How to Take Dark Calibration Frames

Temperature: Must match your lights.

Exposure time: Must match your lights.

ISO/Gain: ISO or Gain